In December 2019, Hayabusa 2 will depart Ryugu for its
year-long journey back to Earth. Just a few hours from home
in December 2020, the return capsule will separate from
the main spacecraft before beginning its 12-km/s reentry
through the atmosphere, ending with a parachute-assisted
landing at the Woomera Test Range in Australia.
Not a Carbon Copy
q NASA'S STRATEGY Expecting a rubble-strewn surface, OsirisREX will forego projectiles when it touches down on Bennu (1). Once
its sampling head is securely planted on the asteroid's surface, it will
release a burst of nitrogen gas (2), kicking up dust and small pebbles
into the instrument. A few seconds after touchdown, the spacecraft
will lift off (3), stowing the sample in its return capsule on the craft's
underbelly (4).
1
2
3
4
OSIRIS-RE X: N ASA; SA MPLING: G REGG DINDER M A N / S&T
In contrast to Hayabusa 2's adventurous multi-vehicle
choreography and blast-and-go sampling, the Osiris-REX
mission team chose a more conservative, single-spacecraft
methodology. Having roared off its Cape Canaveral launch
pad on September 8, 2016, the two-ton spacecraft begins its
approach phase to Bennu in August 2018, during which time
the operations and science teams will begin a search for small
moons and any damaging dust that might orbit the asteroid,
examine the surface, and reﬁne their model of Bennu's shape.
After a few tentative low-speed hyperbolic passes several
kilometers from the asteroid and a couple months in an
initial 1.5-km-high "practice" orbit, Osiris-REX will begin
the detailed survey and reconnaissance phase of its mission
in late February 2019. Its three-camera suite (including an
8-inch telescope) will map the asteroid, provide detailed
context for the sample site, and monitor the progress of the
sample acquisition itself. Meanwhile, a laser altimeter will
produce a ﬁnely detailed topographic map, while three different spectrometers map the mineral, organic, and thermal
lay of the land.
The Touch-And-Go (TAG) sample acquisition strategy is
designed with both spacecraft safety and preservation of the
sample's pristineness in mind. The microgravity environment makes extended spacecraft contact with the surface a
risky venture, especially given that Osiris-REX is about the
size of a walk-in closet and could easily tip over. So, much
like their Japanese colleagues, the Osiris-REX team has
opted for a similar slow descent, brief touchdown, and
get-outta-Dodge plan of action.
This plan centers on the Touch-And-Go Sample
Acquisition Mechanism (TAGSAM), an articulated arm that extends a few meters below the main
structure of the spacecraft. At the business end of the arm
is a large-dinner-plate-size annulus of ﬁne metal mesh,
which makes the instrument look like the combination of
q OSIRIS-REX
INSTRUMENTS
X-ray imaging
spectrometer
Camera
suite
Thermal
emission
spectrometer
Laser altimeter
Visible and IR
spectrometer
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